This invention relates to novel polysaccharide graft polymers containing acetal groups and to the methods for their preparation. It also relates to novel polysaccharide graft polymers containing aldehyde groups and to their preparation from the corresponding acetals. It also relates to the use of the aldehyde-containing graft polymers as wet strength agents in paper. It further relates to novel acetal-containing monomers suitable for use in the polysaccharide graft polymerization.
As used herein, the term "paper" includes sheet-like masses and molded products made from fibrous materials which may be derived from natural cellulosic sources as well as from synthetics such as polyamides, polyesters, and polyacrylic resins, and from material fibers such as asbestos and glass. In addition, papers, made from combinations of cellulosic and synthetic materials are applicable herein. Paperboard is also included within the term "paper".
Oxidative and non-oxidative methods have been used to introduce aldehyde groups into polysaccharides such as starches, gums, and celluloses. The oxidative methods used have included treatment with periodic acid, periodates, or alkali metal ferrates. See U.S. Pat. No. 3,086,969 (issued Apr. 23, 1963 to J. E. Slager); U.S. Pat. No. 3,062,652 (issued Nov. 6, 1962 to R. A. Jeffreys et al.); and U.S. Pat. No. 3,632,802 (issued Jan. 4, 1972 to J. N. BeMiller et al.) The disadvantages of the oxidative method include degradation to lower molecular weight products and the formation of carboxyl groups due to further oxidation of the aldehyde groups. U.S. Pat. No. 3,553,193 (issue Jan. 5, 1973 to D. H. LeRoy et al.) describes an improved method for oxidizing starch using an alkali metal bromite or hypobromite under carefully controlled conditions, which reportedly results in a substantially greater proportion of carbonyl groups (i.e., aldehyde groups) than carboxyl groups.
The non-oxidative methods typically involve the reaction of the polysaccharide with an aldehyde-containing reagent. See. U.S. Pat. Nos. 3,519,618, (issued July 7, 1970 to S. M. Parmerter); U.S. Pat. No. 3,740,391 (issued June 19, 1973 to L. L. Williams et al.); and U.S. Pat. No. 2,803,558 (issued Aug. 20, 1957 to G. D. Fronmuller). Another nonoxidative method involves the acid conversion of acetal-containing polysaccharide derivatives to aldehyde-containing polysaccharide derivatives. See U.S. Pat. No. 4,675,394, filed July 24, 1985 and U.S. Pat. No. 4,703,116 and Feb. 14, 1986.
Polyacrylamide-grafted starch polymers containing aldehyde groups are disclosed in European patent appln. No. 147,380 (published July 3, 1985 with the inventors being D. N. VanEenam). Unlike the glyoxalated starch acrylamides of Williams (U.S. Pat. No. 3,740,391 cited above) the polymers contains polyacrylamide grafted to the starch, but like the Williams product the aldehyde groups are introduced by glyoxalating the resulting product (or treating the product with other reactants containing two or more aldehyde units).
One of the disadvantages of introducing the aldehyde groups directly using an aldehyde-containing reagent, such as glyoxal, is the possibility of the derivative crosslinking prior to use. This is a particular disadvantage when the products are being used to impart temporary wet strength to paper via a crosslinking reaction with the cellulose fibers.
Therefore, there is a need for aldehyde-containing polysaccharide derivatives wherein the method for introducing the aldehyde groups is not dependent on a reaction with an aldehyde-containing reagent or direct oxidation to an aldehyde group.